a) Field of the invention
The present invention relates to an objective lens system for microscopes having a large numerical aperture (NA), and so designed as to favorably correct the paraxial and offaxial aberrations.
b) Description of the prior art
Since it is demanded for objective lens systems for microscopes to have a capability to resolve images of objects almost to the limit of diffraction, severer requirements for correcting aberrations are imposed on the objective lens systems for microscopes to correct aberrations more favorably in the objective lens systems for microscopes than in photographic lens systems for cameras. Further, as compared with condenser lens systems for optical disks, objective lens systems for microscopes must correct the paraxial aberrations up to high portions of images as well as the chromatic aberration, thereby being subjected to severe requirements for correction of the aberrations. For this reason, most of objective lens systems for microscopes have complicated compositions and consist of large numbers of lens elements.
As objective lens systems for microscopes having relatively simple compositions and consisting of small numbers of lens elements, there are known the lens systems disclosed by Japanese Examined Published Patent Applications No. 59527/57, No. 15237/43 and No. 24318/40. However, these objective lens systems for microscopes have the offaxial aberrations such as curvature of field which are not corrected sufficiently and are designed for small numerical apertures.
Further, as the objective lens systems having the compositions similar to that of the objective lens system according to the present invention, there are known the lens systems disclosed by Japanese Unexamined Published Patent Applications No. 111914/58, No. 39564/50, No. 34252/54 and No. 135661/53.
Also in these conventional objective lens systems, the offaxial aberrations are not corrected so favorably though the spherical aberration is corrected favorably.